Joints of pipe which are intended to be used for conveying flammable liquids such as gasoline are commonly configured as a hollow bored tube having pipe coupling means integral with or formed wholly with opposite ends of the tube. For example, opposite ends of a pipe joint may incorporate outwardly extending helical threads for coupling with other similarly configured pipe joints in the formation of a pipe string. Where such threads are present at opposite ends of a pipe joint, pipe coupling typically is accomplished via internally threaded coupling sleeves. As a further example, one end of such pipe joint may incorporate an outwardly extending helical thread, while the opposite end of the joint may include a wholly formed internally threaded bell, such pipe coupling structures allowing multiple identical renditions of such pipe joint to be threadedly attached end to end, forming a liquids conveying pipe string. As further examples, ends of such pipe joints may alternately incorporate longitudinally apertured mounting flanges or radially outwardly extending ridges which are adapted for engaging with and being drawn longitudinally by rotatable coupling nuts.
When such pipe joints are interconnected to form a pipe string for conveyance of flammable liquids, it is often desirable to incorporate within the pipe string means for determining the presence and/or the character of liquids within the bores of the pipe joints. For example, where a pipe string is to be disassembled, the bores of the joints are preferably devoid of flammable liquids. Disassembly of a pipe string which contains a flammable liquid such as gasoline can result in a hazardous chemical spill, or may result in a fire or explosion. Accordingly, operators are desirably provided means for confirming the absence of gasoline within such a pipe string prior to disassembly. Such confirmation is similarly desirable where such a pipe string extends from a tank and is utilized for purging water which on occasion may underlie gasoline within the tank. In that setting, an operator is desirably provided means for detecting the commencement of gasoline flow into pipe string, allowing a shut off valve to be immediately closed upon completion of water purging, and avoiding undesirable filling of the pipe string with gasoline.
The instant inventive pipe joint assembly provides a means for visually confirming the presence or character of liquids within a pipe string as described above, while also providing for mechanical simplicity and economy; the assembly being capable of performing all of the functions of commonly configured pipe joints among a pipe string, and the assembly being installable and disassembleable as easily as such commonly configured pipe joints.